Blowout preventer seal assembly and method of using same

ABSTRACT

A shear sealing system of a blowout preventer of a wellbore is provided. The blowout preventer including a housing having a bore and a guideway therethrough. A tubular of the wellbore is positionable in the bore. The shear sealing system includes at least one carriage, at least one blade and at least one seal. The carriages are slidably positionable in the guideway of the blowout preventer. The blades are carried by the carriages and movable thereby between a retracted position and an extended position. The blades are engageable with the tubular when in the extended position. The seal forms a seal about the tubular and with the blade when the blade is in the extended position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to the U.S. provisional patentapplication Ser. No. 61/502,683 filed on Jun. 29, 2011.

BACKGROUND

This disclosure relates generally to techniques for performing wellsiteoperations. More specifically, this disclosure relates to techniques forpreventing blowouts involving, for example, shearing a tubular and/orsealing a wellbore.

Oilfield operations may be performed to locate and gather valuabledownhole fluids. Oil rigs are positionable at wellsites, and downholetools, such as drilling tools, are deployed into the ground to reachsubsurface reservoirs. Once the downhole tools form a wellbore to reacha desired reservoir, casings may be cemented into place within thewellbore, and the wellbore completed to initiate production of fluidsfrom the reservoir. Downhole tubular devices may be positioned in thewellbore to enable the passage of subsurface fluids to the surface.

Leakage of subsurface fluids may pose an environmental threat ifreleased from the wellbore. Equipment, such as blowout preventers(BOPs), may be positioned about the wellbore to form a seal about atubular therein to prevent leakage of fluid as the fluid is brought tothe surface. BOPs may have selectively actuatable rams or ram bonnets,such as pipe rams or shear rams, that may be activated to sever atubular in a wellbore. Some examples of BOPs for severing tubulars areprovided in U.S. Patent/Application Nos. 20110000670; U.S. Pat. Nos.7,814,979; and 7,367,396. Seals may optionally be provided in BOPs.Examples of seals are provided in US Patent/application Ser. Nos.13/018,217, 2012/0012339, 2012/0012340, 2010/243926, and U.S. Pat. No.7,967,299. Despite the development of techniques for addressingblowouts, there remains a need to provide techniques for shearing atubular and/or sealing a wellbore.

SUMMARY

In at least one aspect, the disclosure relates to a shear sealing systemof a blowout preventer of a wellbore. The wellbore has a tubular thereinand the blowout preventer includes a housing having a bore and aguideway therethrough. The tubular is positionable in the bore. Theshear sealing system includes at least one carriage slidablypositionable in the guideway of the blowout preventer, at least oneblade and at least one seal. The blade is carried by the carriage andmovable thereby between a retracted position and an extended position.The blade is engageable with the tubular when in the extended position.The seal forming a seal about the tubular and with the blade when theblade is in the extended position

The blade may include an upper blade and a lower blade and the seal mayinclude an upper seal and a lower seal. The upper blade, the lowerblade, the upper seal and the lower seal may be placed in sealingengagement. The seal may be positionable in the housing. The seal mayform a metal to metal seal with the blade. The seal may be a tubularmember having an outer diameter positionable along an inner diameter ofthe bore. The seal may have a bottom surface positionable along an innerdiameter of the guideway. The bottom surface may be engageable with atop surface of the blade when the blade moves to the extended position.The seal may include at least one seal collar, at least one coil spring,and/or at least one elastor seal.

The carriage may include a base having a blade pocket for receiving theblade. The base may have spars extending from a front end thereofdefining a seal pocket for receiving the seal. The carriage may includea plurality of carriages and the blade may include a plurality ofblades. Each of the carriages may have a blade pocket for receivinglysupporting a corresponding one of the seals. The seal may include anelastomeric material disposable about each of the carriages. Thecarriages may include a base having a seal pocket shaped to receivinglyand sealingly engage the blades carried by the carriages. The sealpocket may be defined along a top and side surfaces of the base.

In another aspect, the disclosure relates to a blowout preventerpositionable about a wellbore. The wellbore has a tubular therein. Theblowout preventer may include a housing having a bore and a guidewaytherethrough (with the tubular positionable in the bore), and a shearsealing system. The carriage may include upper and lower carriages, theblade may include upper and lower blades and the seal may include upperand lower seals. The upper seals may be positionable in the housingabove the upper blades in sealing engagement therewith, and the lowerseals may be positionable in the housing below the lower blades insealing engagement therewith. The upper seals may be positionable aboutthe upper blades of the upper carriage and the lower seals may bepositionable about the lower blade of the lower carriage. The upperseals may be sealingly engageable with the lower blade and the lowerseals sealingly engageable with the upper blades. The seal may form ametal to metal seal with the blade. The seal may include an elastomericmaterial carried by the carriage and sealable with the blade. Thehousing may have at least one receptacle for receiving the seal.

In another aspect, the disclosure relates to a method of forming a sealabout a tubular of a wellbore. The method involves providing a blowoutpreventer including a housing having a bore and a guideway therethrough(the tubular positionable in the bore) and a shear sealing systemincluding at least one carriage (at least one blade carried by thecarriage and a seal). The method also involves engaging the tubular withthe blade by slidably positioning the carriage in the guideway of theblowout preventer and moving the blade between a retracted position andan extended position, and forming a seal about the tubular and betweenthe seal and the blade when the blade is in the extended position

The engaging may involve shearing the tubular, and the shearing mayinclude piercing, cutting, raking, shaving, and/or severing. The blademay include an upper blade and a lower blade, and the seal an upper sealand a lower seal. The forming may involve forming a seal between theupper blade, the lower blade, the upper seal and the lower seal. Theforming may involve sealingly engaging the upper blade with the lowerseal and sealingly engaging the lower blade with the upper seal, and/orsealing engaging the upper blade with the lower seal and the lower bladewith the upper seal.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features and advantages of the presentdisclosure can be understood in detail, a more particular description ofthe subject matter, briefly summarized above, may be had by reference tothe embodiments thereof that are illustrated in the appended drawings.It is to be noted, however, that the appended drawings illustrate onlyexample embodiments of the subject matter and are, therefore, not to beconsidered limiting of its scope. The figures are not necessarily toscale and certain features, and certain views of the figures may beshown exaggerated in scale or in schematic in the interest of clarityand conciseness.

FIG. 1 shows a schematic view of an offshore wellsite provided with ablowout preventer (BOP) having a shear sealing system for shearing atubular and sealing a wellbore.

FIGS. 2A-2B show schematic side and top views, respectively, partiallyin cross-section, of a BOP having a shear sealing system in a retractedposition.

FIG. 2C is a schematic side view, partially in cross-section, of a BOPhaving a shear sealing system in an extended position.

FIGS. 3A-3B are horizontal and vertical cross-sectional views,respectively, of a BOP having a shear sealing system therein.

FIG. 3C is a schematic view depicting an end view, partially incross-section, of the BOP of FIG. 3B.

FIGS. 4A-4C show perspective views of the shear sealing system of FIGS.3A-3C having a pair of carriages in a retracted, partially extended, andfully extended position about a seal assembly.

FIGS. 5A-5C depict side, top and perspective views, respectively, of analternate seal assembly.

FIG. 5D depicts a perspective view of a portion of the alternate sealassembly of FIG. 5B.

FIG. 6 is a flow chart depicting a method of forming a sealing about atubular of a wellbore.

DETAILED DESCRIPTION

The description that follows includes exemplary apparatus, methods,techniques, and/or instruction sequences that embody techniques of thesubject matter. However, it is understood that the described embodimentsmay be practiced without these specific details.

Blowout preventers (BOPS) may be positioned about a tubular and providedwith devices for shearing a tubular and/or sealing a wellbore. Shearingmay involve piercing, cutting, raking, shaving, severing or otherwisepenetrating at least a portion of the tubular. In some cases, suchshearing involves advancing blades of the BOP into the tubular to breakthe tubular into two pieces. In some cases, such sealing may involvecreating a seal about the severed tubular to prevent fluid from passingfrom the tubular. Such seal may be positioned about the blades used toshear the tubular. Tubulars may be, for example, pipes, certain downholetools, casings, drill pipe, liner, coiled tubing, production tubing,wireline, slickline, or other tubular members positioned in the wellboreand associated components, such as drill collars, tool joints, drillbits, logging tools, packers, and the like.

Such shearing and/or sealing devices may provide a metal-to-metal and/orbi-directional differential pressure barrier against, for example,extreme conditions, such as low/high pressure hydrostatic and gas mediawith an effect temperature range of from about −30 F (−34.40 C) throughabout 400 F (204.44 C) or more. These devices may be intended to provideone or more of the following, among others: reduced operational force,reduced failure, reduced wear, efficient part replacement, modularcomponents, enhanced sealing, efficient shearing, metal-to-metalsealing, incorporation into (or use with) existing equipment and lessmaintenance time for part replacement, operability at extreme conditions(e.g., extreme temperatures and pressures), etc.

FIG. 1 depicts an offshore wellsite 100 having a subsea system 104 and asurface system 102. The surface system 102 may be used to facilitate theoilfield operations at the offshore wellsite 100. The surface system 102may include a rig 105, a platform 106 (or vessel) and a controller 108.

The subsea system 104 includes a conduit 110 extending from the platform106 to a sea floor 112. The subsea system further includes a wellhead114 with a tubular 116 extending into a wellbore 118, a BOP 120 and acontroller 108. The BOP 120 has a shear sealing system 124 for shearingthe tubular 116 and sealing the wellbore, as will be described furtherherein.

The surface system 102 and subsea system 104 may be provided with one ormore controllers 108 located at various locations to control the surfacesystem 102 and/or the subsea system 104. Communication links 126 may beprovided for communication between the controllers 108 and various partsof the wellsite 100.

Although the BOP 120 is described herein as being used in subseaoperations, it will be appreciated that the wellsite 100 may be land orwater based, and the BOP 120 and/or shear sealing system 124 may be usedin any wellsite environment.

FIGS. 2A-2C depict the BOP 120 in greater detail. FIGS. 2A and 2B showthe BOP 120 in the retracted position before actuation. FIG. 2C showsthe BOP 120 in the extended position after actuation. The BOP 120 may besimilar to, for example, the BOP described in U.S. Patent/ApplicationNos. 20110000670; U.S. Pat. Nos. 7,814,979; and 7,367,396, the entirecontents of which are hereby incorporated by reference herein.

As shown in FIGS. 2A-2C, the BOP 120 may have a body 212 with a bore 214extending therethrough. The tubular 116 may pass through the bore 214.The body 212 may have a lower flange 216 and an upper flange 218 forconnecting the BOP 120 to other equipment about the wellsite, such asthe wellhead 114 (FIG. 1). The BOP 120 may have the one or moreactuators 228 for actuating the shear sealing system 124 therein, forexample, in order to shear the tubular 116 and sealing the wellbore.

Each of the actuators 228 may move a piston 230 within a cylinder 232 inorder to move a rod 234. Each rod 234 may couple to a carriage 240 a,bof the shear sealing system 124. Each of the carriages 240 a,b carries ablade 242 a,b. Thus, the actuators 228 may move the blades 242 a,btoward and away from the bore 214 in order to shear the tubular 116within the bore 214. The actuators 228 may actuate the blades 242 a,b inresponse to direct control from the controller(s) 108 (FIG. 1), anoperator, and/or a condition, such as a pressure surge, in the wellbore118 (as shown in FIG. 1). As shown in FIGS. 2A-2C, the actuators 228 maybe hydraulically operated and driven by a hydraulic system (not shown),although any suitable means for actuating the shear sealing system 124may be used, such as pneumatic, electric, and the like.

One or more ram guideways (or guides) 220 and 222 may guide each of thecarriages 240 a,b within the BOP 120 as the actuator 228 moves theblades 242 a,b. The ram guideways 220 and 222 may extend outwardly fromopposite sides of the bore 214. FIG. 2B shows a top view of the BOP 120.The carriages 240 a,b are shown holding the blades 242 a,b in anunactuated (or retracted) position within the ram guideways 220 and 222.

The blades 242 a,b of carriages 240 a,b may be positioned to pass oneanother within the bore 214 while shearing the tubular 116. As shown,the pair of blades 242 a,b includes an upper cutting blade 242 a on thecarriage 240 a and a lower cutting blade 242 b on the carriage 240 b.The blades 242 a,b may be movably positioned so that the upper blade 242a passes some distance above the blade 242 b when shearing the tubular116.

As shown in FIG. 2C, the shearing action of cutting blades 242 a,b maypierce, rake, cut, shave, sever, and/or shear the tubular 116 such thatthe tubular is compressed or separated into upper portion 116 a andlower portion 116 b. After the tubular 116 is severed, the lower portionof the tubular 116 b may drop into the wellbore 118 (as shown in FIG. 1)below the BOP 120. In the closed position, a seal assembly 243 of theshear sealing system 124 positioned in the BOP 120 may form a seal withthe blades 242 a,b.

FIGS. 3A-3C depict various views of a BOP 320 having a shear sealingsystem 324 usable for shearing the tubular 116 and/or sealing thewellbore (see, e.g., FIG. 1). FIGS. 3A and 3B are cross-sectional viewsof the BOP 320 having a bore 314 therethrough for receiving the tubular116 (see, e.g., FIG. 1). The shear sealing system 324 includes acarriage assembly 325 movably positionable in a guideway 321, and a sealassembly 330 positioned in receptacles 331 a,b in the BOP 320.

The guideway 321 extends into the bore 314 to enable movement of thecarriage assembly 325 therein for sealing engagement with seal assembly330 and the tubular 116. As shown in FIG. 3A, the carriage assembly 325is in a retracted (or disengaged) position. As shown in FIG. 3B, thecarriage assembly 325 is advanced to an extended (or engaged) position.The shear sealing system 324 includes a pair of carriages 326 a,b, and apair of blades (or blade inserts) 328 a,b. Each of the carriages 326 a,bcarries a blade 328 a,b such that the blades 328 a,b may be advanced topass through the tubular 116.

The guideway 321 of the BOP 320 may be shaped to slidingly receive thecarriages 326 a,b for back and forth movement therein. The carriages 326a,b may be selectively extended and refracted in the guideway 321 suchthat the blades 328 a,b carried by the carriages 326 a,b may selectivelyengage the tubular 116 in the bore 314. The carriages 326 a,b may beprovided with rails 337 for slidable movement within the guideway 321.The rails 337 (and other components of the shear seal assembly 324) maybe replaceable.

The components of the shear seal assembly 324 may be modular. Forexample, each blade 328 a,b may be inserted into its correspondingcarriage 326 a,b and secured therein by conventional means, such asbolts 329. Each blade 328 a,b may be positioned in the carriage 326 a,bat an end near the bore 314 for engagement with the tubular 116. Theblades 328 a,b may be the same or different blades, such as thosedescribed in U.S. Patent/Application Nos. 20110000670; U.S. Pat. Nos.7,814,979; and 7,367,396, previously incorporated herein by reference.The blades 328 a,b may have protrusions (or points) 333 to first pierceand then shear the tubular 116 during a shearing operation.

During operation, the carriages 326 a,b may be positioned in the BOP 320and advanced such that the blade 328 a passes a distance below the blade328 b to provide shearing engagement with the tubular 116 as shown inthe extended position of FIG. 3B. An actuator (not shown) may be used toactivate the shear sealing system 324 to move the carriages and theblades in a similar manner as shown in FIGS. 2A-2C. As the carriages 326a,b move to the extended position of FIG. 3B, the blades 328 a,b mayalso engage and form a seal with the seal assembly 330.

The seal assembly 330 may be positioned in the receptacles 331 a,b alongthe bore 314 and the guideway 321. The seal assembly 330 includes sealcollars 332 a,b, coil springs 334 a,b, and elastor seals 336 a,b asshown in FIG. 3C. In FIG. 3C, an end view of the carriage assembly 325is depicted adjacent a cross-sectional view of the seal assembly 330 andBOP 320. The seal assembly 330 (and/or its components) may be made ofmetal or non-elastomeric material to prevent deterioration over timeand/or under harsh conditions.

The upper receptacle 331 a has the corresponding upper seal collar 332a, coil spring 334 a and elastor seal 336 a therein. The lowerreceptacle 331 b has the corresponding lower seal collar 332 b, coilspring 334 b and elastor seal 336 b therein. The coil springs 334 a,bmay be used to support the seal collar 332 a,b against the carriages 326a,b (see, e.g., FIG. 3B), particularly in high pressure conditions.Additional seals, such as the elastor seals 336 a,b, may be provided foradditional sealing support about the seal collar 332. Additional sealsmay also be positioned about the shear sealing system to further preventleakage.

The upper and lower seal collars 332 a,b, coil springs 334 a,b, andelastor seals 336 a,b may be used to cooperatively seal with the blades328 a,b to provide a seal about the bore 314. Once the carriages 326 a,bare advanced and the blades 328 a,b engage the seal collars 332 a,b asshown in FIG. 3B, a metal-to-metal seal is formed therebetween. In thisposition, the seal collars 332 a,b are perpendicular to and in sealingengagement with a seal surface 338 a,b of the blades 328 a,b. The coilsprings 334 a,b may be used to provide compressive forces to maintain aconstant interface between the seal collars 332 a,b and seal surfaces338 a,b, for example, to provide low pressure differential sealperformance.

FIGS. 4A-4C depict the shear sealing system 324 in greater detail and ina retracted, partially extended and extended position, respectively. Fordescriptive purposes, the shear sealing system 324 is depicted outsideof the BOP 320 in FIGS. 4A-4C. As shown FIG. 4A, the carriage 326 b isin an inverted and opposing position relative to the carriage 326 a. Theupper seal collar 332 a, coil spring 334 a and elastor seal 336 a arealso inverted from the lower seal collar 332 b, coil spring 334 b andelastor seal 336 b therein.

As further depicted in FIGS. 4A and 4B, each of the carriages 326 a,bincludes a base 440 a,b and a rod 442 a,b. The rods 442 a,b may becoupled to an actuator (not shown), such as the actuator 228 depicted inFIG. 2. The rods 442 a,b are also coupled to the bases 440 a,b forselective extension and retraction thereof.

The bases 440 a,b are shaped for sliding engagement within the guideway321 of BOP 320 (see, e.g., FIGS. 3A-3C). The bases 440 a,b are alsoshaped such that they may pass adjacent to each other as shown in FIGS.4B-4C and to facilitate sealing with the seal assembly 330. The base 440includes a pair of side portions 444 with a rear portion 446therebetween. The base 440 also defines a blade pocket 447 for receivingand supporting a blade 328 a,b. The blade pocket 447 may be configuredto support the blades 328 a,b such that loads are applied to the base440 to support the blades during operation. The rear portion 446 may beconnected to the rod 442 a,b and provide a platform for receiving theblades 328 a,b.

The pair of side portions 444 may extend a distance beyond the rearportion 446 and/or the blades 328 a,b to define spars (or supports) 445on an end of the side portions 444 that form a seal pocket 448therebetween for receiving the seal collars 332 a,b (see, e.g., FIGS.3A-3C). The seal collars 332 a,b are nestled into a staging position bythe spars 445 to position the seal collar 332 in a readied state of use.The side portions 444 may also have a shoulder 450 for engagement withthe seal collar 332.

The seal collar 332 has a series of ribbed convolutions 452circumferentially positioned on an outer surface thereof forfacilitating sealing therewith. These convolutions 452 may be used, forexample, to help form the metal-to-metal seal profile against the matingblade seal surface in the event of interference, such as misalignment ortrapped debris.

One or more redundant or secondary elastomeric seals, such as elastor336 a,b, may be provided to further reinforce and/or prevent leakage ofthe seal collar 332 a,b. Such redundant seals may be used to furtherbias the seal collar 332 a,b towards the seal surface 338 a,b. Themetal-to-metal interface of the seal assembly 330 may be self energizingto provide support during operation. Secondary elastomer seals, such aselastors 336 a,b, may be reactive to wellbore pressure to enhance sealcharacteristics as wellbore pressures increase. Positioning thecomponents of the seal assembly 330 both above and below the carriageassembly 325 may be used to create a bidirectional seal arrangement.

The shear sealing system as provided herein may be provided with variousfeatures, such as modular independent components that may be replacedindependently regarding service life or wear condition. The shearsealing system may also provide a metal-to-metal primary sealinginterface between components, such as seal assembly 330 and carriageassembly 325. Additional sealing components, such as elastors 336 a,band/or other seals (of elastomeric or other materials) may optionally beprovided.

FIGS. 5A-5D depict an alternate shear sealing system 524 usable, forexample, as the shear sealing system 124 of FIG. 1. The shear sealingsystem 524 is similar to the shear sealing system 324, except that theshear sealing system 524 includes a pair of carriages 526 a,b, and apair of blades (or blade inserts) 528 a,b with seals 530 a,b on thecarriages 526 a,b. Each of the carriages 526 a,b carries a blade 528 a,bsuch that the blades 528 a,b may be advanced to pass through the tubular116.

In this version, each of the carriages 526 a,b has a top surface 552a,b, a bottom surface 554 a,b and a side surface 556 a. A blade pocket558 a,b is formed about the top surface 552 a,b for receiving the blade538 a,b. A seal pocket 560 a,b is formed about the bottom surface 554a,b to receive the blade 538 b,a of the other carriage 526 b,a. Each ofthe seal pockets 560 a,b has a receiving edge 562 a,b that conforms tothe profile of the blade 538 a,b it is receiving to form a sealtherewith.

The side surfaces 556 a,b extend a distance from the receiving edge 562a,b to receivingly engage sides of the blades 538 a,b to extend the sealthereabout. The side surfaces 556 a,b may extend sufficiently to engagethe seal 530 b,a of the other carriage 526 b,a. As shown, the seals 530a,b may extend over at least a portion of each carriage 526 a,bsufficient to provide a seal about the blades 538 a,b and/or carriage526 a,b. When the blades 538 a,b are moved to the extended position(see, e.g., FIGS. 2C and 3B), a seal is formed about the blades (e.g.,along the cutting profile and along the sides of the blades). The seals530 a,b may be made of an elastomeric material (e.g., rubber) to form aseal with the blades 528 a,b.

Additional coverage may also optionally be provided about the BOP. Forexample, one or more of the seals 330 can be used alone, separately orin combination with one or more of the seals 530 a,b. Variouscombinations of the shear sealing system 324 and the shear sealingsystem 524 may be provided.

In operation, as shown in FIG. 6, the shear sealing systems may be usedin a method 670 of forming a seal about a tubular of a wellbore. Themethod involves providing 672 a blowout preventer including a housingand a shear sealing system. The housing has a bore and a guidewaytherethrough. The tubular is positionable in the bore. The shear sealingsystem may include at least one carriage, at least one blade carried bythe carriage and at least one seal. The method may also involve engaging674 the tubular with the blade by slidably positioning the carriage inthe guideway of the blowout preventer and moving 676 the blade between aretracted position and an extended position, and forming a seal aboutthe tubular with the seal.

The engaging may involve shearing the tubular. The shearing may involvepiercing, cutting, raking, shaving, and/or severing the tubular. Theforming may involve sealingly engaging the upper blade with the upperseal and sealingly engaging the lower blade with the lower seal,sealingly engaging the upper blade with the lower seal and the lowerblade with the upper seal, and/or forming a seal between the housing andthe blade.

The method may be performed in any order, and repeated as desired.

It will be appreciated by those skilled in the art that the techniquesdisclosed herein can be implemented for automated/autonomousapplications via software configured with algorithms to perform thedesired functions. These aspects can be implemented by programming oneor more suitable general-purpose computers having appropriate hardware.The programming may be accomplished through the use of one or moreprogram storage devices readable by the processor(s) and encoding one ormore programs of instructions executable by the computer for performingthe operations described herein. The program storage device may take theform of, e.g., one or more floppy disks; a CD ROM or other optical disk;a read-only memory chip (ROM); and other forms of the kind well known inthe art or subsequently developed. The program of instructions may be“object code,” i.e., in binary form that is executable more-or-lessdirectly by the computer; in “source code” that requires compilation orinterpretation before execution; or in some intermediate form such aspartially compiled code. The precise forms of the program storage deviceand of the encoding of instructions are immaterial here. Aspects of thesubject matter may also be configured to perform the described functions(via appropriate hardware/software) solely on site and/or remotelycontrolled via an extended communication (e.g., wireless, internet,satellite, etc.) network.

While the embodiments are described with reference to variousimplementations and exploitations, it will be understood that theseembodiments are illustrative and that the scope of the inventive subjectmatter is not limited to them. Many variations, modifications, additionsand improvements are possible. For example, one or more shear sealingsystems may be used in a BOP to shear a tubular and/or seal a wellbore,and one or more carriages and blades may be used in a shear sealingsystem.

Plural instances may be provided for components, operations orstructures described herein as a single instance. In general, structuresand functionality presented as separate components in the exemplaryconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements may fall within the scope ofthe inventive subject matter.

What is claimed is:
 1. A shear sealing system of a blowout preventer ofa wellbore, the wellbore having a tubular therein, the blowout preventercomprising a housing having a bore and a guideway therethrough, thetubular positionable in the bore, the shear sealing system comprising:at least one carriage slidably positionable in the guideway of theblowout preventer; at least one blade carried by the at least onecarriage and movable thereby between a retracted position and anextended position, the at least one blade engageable with the tubularwhen in the extended position; and at least one seal forming a sealabout the tubular and with the at least one blade when the at least oneblade is in the extended position.
 2. The shear sealing system of claim1, wherein the at least one blade comprises an upper blade and a lowerblade and the at least one seal comprises an upper seal and a lowerseal, and wherein the upper blade, the lower blade, the upper seal andthe lower seal are positionable in sealing engagement.
 3. The shearsealing system of claim 1, wherein the at least one seal forms a metalto metal seal with the at least one blade.
 4. The shear sealing systemof claim 1, wherein the at least one seal is positionable in thehousing.
 5. The shear sealing system of claim 4, wherein the at leastone seal is a tubular member having an outer diameter positionable alongan inner diameter of the bore.
 6. The shear sealing system of claim 5,wherein the at least one seal has a bottom surface positionable along aninner diameter of the guideway, the bottom surface engageable with a topsurface of the at least one blade when the at least one blade moves tothe extended position.
 7. The shear sealing system of claim 4, whereinthe at least one seal comprises at least one seal collar.
 8. The shearsealing system of claim 7, wherein the at least one seal collar hasconvolutions on an outer surface thereof.
 9. The shear sealing system ofclaim 4, wherein the at least one seal comprises at least one coilspring
 10. The shear sealing system of claim 4, wherein the at least oneseal comprises at least one elastor seal.
 11. The shear sealing systemof claim 1, wherein the at least one carriage comprises a base having ablade pocket for receiving the at least one blade.
 12. The shear sealingsystem of claim 11, wherein the base has spars extending from a frontend thereof defining a seal pocket for receiving the at least one seal.13. The shear sealing system of claim 1, wherein the at least onecarriage comprises a plurality of carriages and the at least one bladecomprises a plurality of blades, each of the plurality of carriageshaving a blade pocket for receivingly supporting a corresponding one ofthe plurality of seals.
 14. The shear sealing system of claim 13,wherein the at least one seal comprises an elastomeric materialdisposable about each of the plurality of carriages.
 15. The shearsealing system of claim 13, wherein each of the plurality of carriagescomprises a base having a seal pocket shaped to receivingly andsealingly engage one of the plurality of blades carried by one of theplurality of carriages.
 16. The shear sealing system of claim 15,wherein the seal pocket is defined along a top and side surfaces of thebase.
 17. A blowout preventer positionable about a wellbore, thewellbore having a tubular therein, comprising: a housing having a boreand a guideway therethrough, the tubular positionable in the bore; and ashear sealing system, comprising: at least one carriage slidablypositionable in the guideway of the blowout preventer; at least oneblade carried by the at least one carriage and movable thereby between aretracted position and an extended position, the at least one bladeengageable with the tubular when in the extended position; and at leastone seal forming a seal about the tubular and with the at least oneblade when the at least one blade is in the extended position.
 18. Theblowout preventer of claim 17, wherein the at least one carriagecomprises upper and lower carriages, the at least one blade comprisesupper and lower blades and the at least one seal comprises upper andlower seals.
 19. The blowout preventer of claim 18, wherein the upperseals are positionable in the housing above the upper blades in sealingengagement therewith, and wherein the lower seals are positionable inthe housing below the lower blades in sealing engagement therewith. 20.The blowout preventer of claim 18, wherein the upper seals arepositionable about the upper blades of the upper carriage and the lowerseals are positionable about the lower blade of the lower carriage, theupper seals sealingly engageable with the lower blade and the lowerseals sealingly engageable with the upper blades.
 21. The blowoutpreventer of claim 17, wherein the at least one seal forms a metal tometal seal with the at least one blade.
 22. The blowout preventer ofclaim 17, wherein the at least one seal comprises an elastomericmaterial carried by the at least one carriage and sealable with the atleast one blade.
 23. The blowout preventer of claim 17, wherein thehousing has at least one receptacle for receiving the at least one seal.24. A method of forming a seal about a tubular of a wellbore, the methodcomprising: providing a blowout preventer, comprising: a housing havinga bore and a guideway therethrough, the tubular positionable in thebore; and a shear sealing system comprising at least one carriage, atleast one blade carried by the at least one carriage and at least oneseal; engaging the tubular with the at least one blade by slidablypositioning the at least one carriage in the guideway of the blowoutpreventer and moving the at least one blade between a retracted positionand an extended position; and forming a seal about the tubular andbetween the at least one seal and the at least one blade when the bladeis in the extended position.
 25. The method of claim 25, wherein theengaging comprises shearing the tubular.
 26. The method of claim 26,wherein the shearing comprises one of piercing, cutting, raking,shaving, severing and combinations thereof.
 27. The method of claim 25,wherein the at least one blade comprises an upper blade and a lowerblade and the at least one seal comprises an upper seal and a lowerseal, and wherein the forming comprises forming a seal between the upperblade, the lower blade, the upper seal and the lower seal.
 28. Themethod of claim 28, wherein the forming comprises sealingly engaging theupper blade with the upper seal and sealingly engaging the lower bladewith the lower seal.
 29. The method of claim 28, wherein the formingfurther comprises sealing engaging the upper blade with the lower sealand the lower blade with the upper seal.